The invention set forth in this specification is directed to complete or composite circuits which are primarily intended for use in electrically heated desoldering equipment. The invention, however, is considered to be of broader scope than such utilization. In its broader aspects the invention relates to coil operation circuits such as may be utilized in controlling the operation of a load such as a solenoid or relay coil. It also relates to such coil operation circuits utilized in combination with operating circuits enabling a single switch in a series circuit to be utilized to control whether or not power is supplied to the coil while the series circuit is utilized for its intended purpose of supplying power to a load.
The circuits in accordance with this invention are considered to be particularly desirable for use in electrically heated desoldering equipment constructed so as to include a hand-held manipulative desoldering tool and an associated structure utilized to supply a vacuum to the desoldering tool and utilized to regulate the amount of heat given off by a heating element in such a tool. Such tools are commonly constructed so that a tube capable of being used in conjunction with a vacuum to "suck up" solder is located within the tool so as to extend through the center of the heating element. In order to facilitate the use of such a tool an appropriate control is normally employed so as to regulate when a vacuum is supplied to such a tube. Such a control is desired so that the vacuum will be used only when solder to be removed has been melted through the use of the heating element.
Several problems have been encountered in incorporating a control for the application of a vacuum to a manipulative desoldering tool as indicated in the preceding discussion. In order to minimize the size of the tool so as to facilitate the ease with which the tool may be used it is desired to minimize the number of components within the tool to the greatest possible extent. Further, it is normally desired to utilize as few electrical conductors or tubes leading to the tool as reasonably possible. These considerations are considered to make the prior utilizations of vacuum control valves within such tools and the prior utilization of control wires for separately controlling the application of a vacuum in desoldering tools comparatively undesirable. It is not considered that an understanding of the present invention requires a detailed explanation of such prior structures utilizing mechanical vacuum control valves in a tool and/or a detailed discussion of the disadvantages of using conventional switches to remotely control a vacuum in a tool as noted.